This invention relates to bis-(4-isocyanatophenoxy)-alkanes, bis-(4-isocyanato-3-methyl-phenoxy)alkanes and to a process for the production thereof.
The properties of polyurethane plastics, in particular of polyurethane elastomers, are essentially dependent upon the nature of the polyisocyanate used in their production. Aromatic diisocyanates, such as 4,4'-diisocyanato-diphenylmethane, tolylene diisocyanate and 1,5-diisocyanatonaphthalene are typically used in the production of polyurethane elastomers (see, e.g., Becker, Braun, Kunststoff-Handbuch, Vol. 7, 2nd Edition (1983), Carl Hanser Verlag, pages 391 et seq).
Although 4,4'-diisocyanato-diphenylmethane and tolylene diisocyanate produce elastomers inexpensively, the elastomers obtained often have unsatisfactory mechanical and thermal properties. High-grade polyurethane elastomers may, for example, be obtained if 1,5-diisocyanatonaphthalene is used as the diisocyanate component. Cast elastomers based on this diisocyanate are distinguished by excellent mechanical properties.
However, 1,5-diisocyanatonaphthalene suffers from the disadvantage that the crude material used for the production thereof, naphthalene, is available only in limited quantities. Furthermore, the nitration of naphthalene inevitably leads to an isomer mixture of nitronaphthalenes from which 1,5-dinitronaphthalene must be isolated. The purification by distillation of 1,5-diisocyanatonaphthalene obtained from the dinitro compound (by hydrogenation and subsequent phosgenation of the resulting diamine) is difficult because 1,5-diisocyanatonaphthalene tends to sublimate. This means that 1,5-diisocyanatonaphthalene is expensive.
The processing of 1,5-diisocyanatonaphthalene is often difficult because its melting point and vapor pressure are relatively high. These properties often do not permit 1,5-diisocyanatonaphthalene to be reacted directly as melt. Technically costly processing methods and protective measures are then required to prevent chemical and operational problems.
Many attempts have been made to find a comparable alternative to 1,5-diisocyanatonaphthalene as a diisocyanate component in the production of high-grade polyurethane plastics. For example, German Offenlegungsschriften Nos. 3,138,421 and 3,138,422 describe the production of polyurethane elastomers using 4,4'-diisocyanato-(1,2)-diphenylethane as the diisocyanate component. Admittedly, plastics with good mechanical properties can be obtained with this diisocyanate, but the production of 4,4'-diisocyanato-diphenyl-ethane-(1,2) is very involved and costly and hitherto difficult to realize commercially.
Many attempts have been made to use the comparatively inexpensive 4,4'-diisocyanato-diphenylmethane instead of 1,5-diisocyanatonaphthalene for the production of high-grade polyurethane elastomers. However, all of these attempts have failed to produce polyurethane elastomers based on this diisocyanate which have mechanical and thermal properties corresponding to 1,5-diisocyanatonaphthalene-based polyurethane elastomers.